enhance(emoji): update to Unicode 17, unify and lazy-load emoji data (#39363)

Generate emoji data from Unicode 17's `emoji-test.txt`, keeping existing
aliases. `public/assets/emoji.json` is now the single emoji data file,
also loaded by the backend. Rendered emoji drop their `aria-label`, the
dark theme inverts key on a new `data-alias` attribute instead.

Skin tone variants and their Gitea-only aliases are removed, GitHub has
none either.

Emoji autocompletion is now lazy-loaded with the markdown editor,
shrinking the index JS chunk from 653KB to 563KB.

---------

Signed-off-by: silverwind <me@silverwind.io>
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: bircni <bircni@icloud.com>

Makefile

@@ -637,6 +637,10 @@ lockfile-check:
 generate-gitignore: ## update gitignore files
 	$(GO) run build/generate-gitignores.go
 
+.PHONY: generate-emoji
+generate-emoji: ## update emoji data from Unicode
+	$(GO) run build/generate-emoji.go
+
 .PHONY: generate-images
 generate-images: | node_modules ## generate images
 	cd tools && node generate-images.ts $(TAGS)